The invention relates to a stack of interferential thin layers at least partially reflecting in the infrared, especially that emitted by solar radiation, and which comprises at least one xe2x80x9cfunctionalxe2x80x9d layer and coatings of dielectric material which are placed on each side of the latter.
The expression xe2x80x9cfunctional layer(s)xe2x80x9d is understood within the invention to mean the layer or layers which, within the stack, have the desired thermal reflection properties and which are metallic, more particularly based on a noble metal of the Ag type.
The expression xe2x80x9ccoatings of dielectric materialxe2x80x9d is understood within the invention to mean a layer or a superposition of layers of dielectric material of the metal oxide, metal nitride or silicon nitride type, especially having the function of adjusting the optical appearance of the stack, especially of lowering the light reflection, and optionally the function of protecting the xe2x80x9cfunctionalxe2x80x9d layer or layers.
Thus, the present invention relates to stacks of the type:
(dielectric coating/functional layer/dielectric coating)
this sequence being possibly repeated n times, with n=2 or 3.
The invention concerns multilayer stacks on a rigid substrate of the glass or rigid polymer, such as polycarbonates PC or polymethyl methacrylate PMMA, type. It is possible to use substrates in glazing units, by themselves or mounted as insulating or laminated glazings. However, the invention relates more particularly to flexible substrates based on polymer, especially polyurethane PU or polyethylene terephthalate.
Studies have already been carried out on stacks comprising silver layers interspersed with AlN and/or metal-oxide dielectrics, these multilayer stacks being deposited on PET substrates. Reference may especially be wade to Patent Application PCT/FR99/00466 filed on Mar. 2, 1999 in the name of Saint-Gobain Vitrage.
It is advantageous for all or some of the dielectric coatings used to be based on a nitride, especially the two most common in this application, namely aluminium nitride AlN or silicon nitride Si3N4. This is because nitride-based dielectrics are particularly stable chemically and can thus effectively fulfil the role of xe2x80x9cbarrier layerxe2x80x9d with respect to the silver layer or layers. It is therefore advantageous to place them at least as a xe2x80x9csublayerxe2x80x9d directly on the substrate and/or as an xe2x80x9coverlayerxe2x80x9d as the final layer of the stack.
However, their use is not without drawbacks: this is because it has been found that their adhesion to silver is not optimal, which results, moreover, in the stack being quite fragile, with the risk of delamination and problems of optical quality. One possibility of increasing this mutual adhesion consists in interposing, between the silver layer and the nitride layer, a thin layer which will act as an adhesion layer, this thin layer being, for example, made of a metal of the Ti type, which does not necessarily have to be continuous. This possibility gives good results, but increases the number of layers in the stack.
The object of the invention is therefore to remedy the abovementioned drawbacks, especially to improve the quality of the stacks of thin layers comprising both silver-based layers and nitride-based layers, without causing difficulties or complications in their manufacture on an industrial scale.
The subject of the invention is firstly a flexible or rigid, transparent substrate provided with a stack of thin layers, which includes at least one functional layer predominantly based on silver Ag placed between two coatings of dielectric material, at least one of the coatings comprising a layer predominantly based on aluminium nitride AlN. According to the invention, the functional layer (or at least one of the functional layers) is chemically modified by incorporating at least one minor metal M other than Ag.
Alternatively or in addition, the AlN-based layer (or at least one of the AlN-based layers) is also chemically modified by incorporating at least one minor metal Mxe2x80x2 other than aluminium Al.
The metal M and the metal Mxe2x80x2 may be incorporated by using (as moreover for all the other layers in the stack) the known vacuum deposition technique of sputtering, preferably magnetic-field-enhanced sputtering: what is then provided is, respectively, a silver target alloyed with the metal M in question (deposition in an inert atmosphere, possibly containing nitrogen) and an aluminium target alloyed with the metal Mxe2x80x2 in question (deposition of the nitride in a nitriding reactive atmosphere, containing nitrogen).
The term xe2x80x9cmetalxe2x80x9d within the meaning of the invention includes silicon. To make the targets, the alloy may be made in a known manner by sintering a mixture of powders of the metals in question. The Al target may also be partially covered with the metal in question.
It has thus proved possible to increase the affinity between the silver and the metal nitrides, such as AlN, by slightly modifying one or both, this modification being sufficient for them to adhere significantly better to each other, but being sufficiently moderate not to cause any deterioration in the desired properties of these materials (optical and thermal properties). It is thus conceivable to dispense with additional layers being interposed between them to facilitate their mutual adhesion, this being a great advantage from the industrial standpoint since the fewer the number of layers, the greater the production efficiency and the more compact the production line may be.
The invention applies most particularly to stacks containing n functional layers and (n+1) dielectric coatings with: nxe2x89xa71, especially n=1, n=2 or n greater than 2. As recalled in the preamble of this text, the substrates may be rigid or flexible.
The metal M that can be incorporated into the silver-based layer is aluminium, copper or gold. Preferably, between 0.1 and 10%, especially between 0.5 and 2%, by weight of the metal M is added to the silver layer.
The metal Mxe2x80x2 that can be incorporated into the AlN-based layer is chosen from at least one of the following metals: Zn, Ti, Sn, Mn, Mg, Ag. It is preferred to add approximately 0.1 to 10%, especially 0.5 to 2%, by weight of the metal Mxe2x80x2 with respect to the aluminium of the layer.
The first preferred embodiment according to the invention consists in the stack comprising at least one silver-based functional layer modified according to the invention, which layer is contiguous with a standard layer at least based on AlN (or one which is also modified according to the invention): in this case, it is more a question of adapting the Ac layer to the AlN layer.
The second preferred embodiment according to the invention, as an alternative or in addition to the first embodiment, consists in the stack comprising at least one AlN-based layer modified according to the invention, which layer is contiguous with a standard silver-based functional layer (or one which is also modified according to the invention). The reverse approach is adopted here, in which it is more a question of seeking to make the AlN more xe2x80x9ccompatiblexe2x80x9d with the silver.
One possible variant of the invention consists in placing the functional layer (or at least one of them or each of them if the stack comprises more than one of them) so as to be in contact on one of its faces with an AlN layer (one of the two layers or both of them being modified according to the invention), the other face of the functional layer being in contact with a layer of a metal oxide or of a mixture of metal oxides, such as ZnO, TiO2, SnO2, Nb2O5, Ta2O5. As the aforementioned PCT patent application stresses, it is in fact advantageous, optionally, to provided, beneath the silver-based layers, layers made of an oxide of the ZnO type which provide very intimate contact with the silver.
This oxide layer may be the last of a superposition of oxide and/or nitride layers, such as AlN or Si3N4 layers.
Another variant (which can be added to the previous one) consists in placing the AlN layer modified according to the invention so as to be in direct contact with the silver layer and to have a greater concentration of metal Mxe2x80x2 near its interface with this silver layer. In other words, it is possible to have a concentration gradient of metal Mxe2x80x2 in the AlN layer, with a concentration increasing towards the AlN/Ag interface. The industrially simplest embodiment consists in fact in dividing the AlN layer into several xe2x80x9cstrataxe2x80x9d, the closest stratum to the silver layer being the richest in metal Mxe2x80x2 (obtained from an Al-Mxe2x80x2 target) and the rest of the layer being depleted in metal Mxe2x80x2 or even completely devoid of metal Mxe2x80x2 (Al target). Thus, it is possible to have the following bilayer structure:
AlN:Mxe2x80x2/AlN or AlN/Mxe2x80x2:AlN. 
This is because it can be slightly prejudicial in terms of light absorption to have AlN containing a metal whose nitride is relatively absorbent (as is the case with titanium for example) over a significant thickness. Thus, by xe2x80x9cduplicatingxe2x80x9d the layer it is possible to increase the adhesion to silver without any risk of optically degrading the stack.
There are three non-limiting embodiments of the invention with two silver layers:
the sequence: substrate/metal oxide/Ag(1)/metal oxide/Ag(2)/AlN
the sequence: substrate/AlN/Ag(1)/metal oxide/Ag(2)/AlN
the sequence: substrate/Ag(1)/AlN/Ag(2)/AlN.
In all three cases, when there is direct contact between AlN and Ag, one or both of them is modified according to the invention. The term xe2x80x9cmetal oxidexe2x80x9d is understood to mean a layer of a metal oxide or several different oxides, or a nitride layer AlN or Si3N4 xe2x80x9cflankedxe2x80x9d by oxide layers (or thin layers of metal of the Ti or NiCr type).
In the simplest variant with a metal oxide layer, TiO2 is especially preferred.
It remains within the scope of the invention for one of the Ag functional layers not to follow the teaching of the invention, unlike the other, and to be, for example, in contact with an AlN or Si3N4 layer via a thin layer intended to increase their mutual adhesion, for example a titanium layer.
It is also possible within the scope of the invention to substitute an AlN layer or at least one of them with an Si3N4 layer, which may be chemically modified like the AlN.
The subject of the invention is also any glazing which incorporates the multilayer-coated substrate described above. In particular, this is laminated glazing using a PET-type flexible substrate coated with the layers according to the invention and laminated by means of two thermoplastic adhesive sheets of the polyvinyl butyral (PVB) or ethylene/vinyl acetate (EVA) type with two glass-type rigid substrates.
The glazing of the invention, whether monolithic, laminated or mounted as insulating double glazing, may be used in buildings or for equipping vehicles, especially as laminated side windows or windscreens.
The invention will be described below with the aid of specific non-limiting examples.
All the layers are deposited in a known way, by sputtering, on a PET sheet having a thickness of approximately 50 micrometers (this sheet being biaxially oriented in a known manner).